1. Field of the Invention
The invention relates to a hydraulic control system with a pipeline antiburst safety device for a double acting drive cylinder for adjusting and securing the position of a machine part, more particularly a driven guide roller in the strand guide of a continuous casting plant, where such machine part exerts an operationally conditioned reaction force on the piston of the cylinder.
2. Discussion of Related Art
Drive cylinders, which do not perform any motion in their operating state, and therefore have merely a "pressure retaining function" can be protected, in the simplest case by means of a non-return valve, against a pipe burst in a pressurized pipeline. Inflow to the cylinder delivery surface is possible but reverse flow in the event of a pipe burst is prevented by virtue of the non-return valve valve cone being already in the closed position. The safety function is insured without the non-return valve performing a control function. If the working pressure in the pressurized pipeline upstream of the non-return valve has collapsed as a result of a pipe burst, it is possible for the pressure required on the cylinder delivery surface to be maintained by means of a pressure retaining accumulator which is connected via an additional non-return valve to the interconnecting pipeline between the pipeline antiburst non-return valve and the drive cylinder.
However, in cases in which the drive cylinder is to "breathe" during its operating state or is even to move to maintain a constant pressure, it will be necessary for the drive cylinder to be connected to the pressure source via an opened valve, for example, an unlockable non-return valve, which said valve must be kept open during normal operation and is closed in the event of a pipe burst by an active control function. This control function is triggered by a signal which depends on pressure drop or a change of volumetric flow. During the time which elapses between a pipe burst and the controlled closing of the unlockable non-return valve, the cylinder surface of the drive cylinder will be subjected to a brief pressure drop, combined with a deflection of the cylinder piston, until the pressure in the drive cylinder is restored after the stop valve is closed.
Such a retraction of the piston in a hydraulic adjusting cylinder is particularly undesirable if the drive cylinder is used for adjusting and securing the position of a driven guide roller in the strand guide of a continuous casting plant. Retraction of the strand guide rollers in this region as a result of a pipe fracture leads to strand bulges and strand fractures, usually entailing a prolonged stoppage of the continuous casting plant. Since the drive cylinders of the guide rollers in a strand guide are connected via opened control valves to the pressure source during the casting process, which said pressure source normally comprises pressure control pumps and a system of pressure accumulators, in order to compensate for internal and external leakages in the control system and on the cylinder, it follows that in addition to the previously mentioned disadvantages concerned with the retraction of the guide rollers, such a pipe or hose burst also results in pressure medium being discharged from the bursting place until the attention of the operating personnel is directed to the burst. The discharging hydraulic fluid may be the cause of a fire since the burst usually occurs near the strand which is still red hot.